Positioning device, electronic instrument, and storage medium storing program

ABSTRACT

A slice set for a specific period of time is acquired from a storage area of a memory which is a ring buffer while changing the read position, and the signal strength total value of each slice set is calculated. The signal strengths of the slices included in the maximum strength slice set and the signal strengths of the slices preceding or subsequent to the maximum strength slice set are calculated, and the final signal read position is determined based on a read offset of the maximum strength slice. A GPS satellite signal is acquired and tracked based on the slice read from the determined signal read position, and a specific positioning process is performed.

This is a continuation application of U.S. patent application Ser. No.12/708,026, which claims priority to U.S. patent application Ser. No.11/839,624 and Japanese Patent Application No. 2006-290819 filed on Aug.16, 2007 and Oct. 26, 2006 respectively. The entire disclosure of U.S.patent application Ser. Nos. 12/708,026 and 11/839,624, and JapanesePatent Application No. 2006-290819 is hereby incorporated herein byreference.

BACKGROUND OF THE INVENTION

The present invention relates to a positioning device, an electronicinstrument, and a storage medium storing a program.

A global positioning system (GPS) is widely known as a satellitepositioning system, and is utilized for a car navigation system and thelike. The GPS allows the present position to be located byacquiring/tracking a GPS satellite signal from signals received from aplurality of GPS satellites, and performing positioning calculationsbased on a navigation message acquired from the GPS satellite signal andthe like.

The GPS satellite signal is a spread-spectrum-modulated signal called acoarse and acquisition (C/A) code. A method has been widely used whichimproves the signal reception sensitivity by correlating a pseudo spreadcode (code replica) generated by a receiver and the received signal overa long period of time when acquiring the GPS satellite signal.

However, since the polarity of the received signal is reversed every 20milliseconds (ms) according to the navigation message, when the signalused for the correlation calculation is acquired across the polarityinversion portion, the signal component is necessarily cancelled(hereinafter called “cancellation portion”). This hinders an appropriatecorrelation process, whereby the signal reception sensitivity(hereinafter simply called “sensitivity”) decreases.

JP-A-2005-321298 discloses technology which sequentially acquiressignals while changing the signal acquisition timing from the signalreception start timing by a predetermined unit time, and selects thesignal with the smallest cancellation portion.

However, since the technology disclosed in JP-A-2005-321298 uses a fixedunit time, the selected signal is cancelled to a large extent when theunit time is increased. For example, since a cancellation portion of upto 2.5 milliseconds occurs when the unit time is set at fivemilliseconds, the sensitivity cannot be increased.

On the other hand, the cancellation portion of the signal decreases byreducing the unit time. However, since the number of signals which mustbe calculated increases, the processing time increases to a largeextent.

SUMMARY

According to one aspect of the invention, there is provided apositioning device comprising:

a memory which is a ring buffer which includes a storage area capable ofstoring three or more cycles of a signal corresponding to at least aninversion time interval of a navigation message and in which a signalreceived by an RF reception circuit section which receives a GPSsatellite signal is sequentially stored while shifting a storageposition; and

a positioning section which reads the signal from the storage area whilechanging a signal read position, performs an acquisition and/or trackingprocess of the GPS satellite signal based on the read signal, andperforms a specific positioning process.

According to another aspect of the invention, there is provided apositioning device comprising:

a memory which is a ring buffer in which a signal received by an RFreception circuit section which receives a GPS satellite signal issequentially stored;

a set-unit signal strength calculation section which calculates a signalstrength of each of M (M≧2) specific-time signal sets obtained atintervals of a specific set-to-set offset time, one specific-time signalset including N (N≧2) specific-time signals obtained from the storagearea at intervals of a specific unit offset time;

a specific-time signal strength calculation section which calculates 1)the signal strength of each of the specific-time signals included in thespecific-time signal set having a maximum strength calculated by theset-unit signal strength calculation section, or 2) the signal strengthof each of the specific-time signals included in the specific-timesignal set having the maximum strength and the specific-time signalspreceding or subsequent to the specific-time signal set having themaximum strength; and

a determination section which determines the read position from thememory used for the correlation process based on the position of thememory at which the specific-time signal is stored which has the maximumstrength calculated by the specific-time signal strength calculationsection;

the positioning device acquiring the GPS satellite signal by reading thesignal from the read position determined by the determination sectionand performing the correlation process, and performing a specificpositioning process.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

FIG. 1 is a block diagram showing the configuration of a portabletelephone.

FIG. 2 is a view illustrative of the outline of a process performed by abaseband process circuit section.

FIG. 3A is a view showing the configuration of a memory, and FIGS. 3Band 3C are views illustrative of a data write operation.

FIG. 4 is a view illustrative of a signal read operation.

FIG. 5 is another view illustrative of a signal read operation.

FIG. 6 is a view illustrative of a read target range.

FIG. 7A is a view showing results obtained in a strong electric fieldenvironment, and FIG. 7B is a view showing results obtained in a weakelectric field environment.

FIG. 8A is a view showing the configuration of a ROM, and FIG. 8B is aview showing the configuration of a RAM.

FIG. 9 is a view showing a data configuration example of satellite-unitmaximum strength read offset data.

FIG. 10 is a view showing a data configuration example of satellitedata.

FIG. 11 is a flowchart showing the flow of a baseband process.

FIG. 12 is a flowchart showing the flow of a maximum strength readoffset determination process.

DETAILED DESCRIPTION OF THE EMBODIMENT

According to one embodiment of the invention, there is provided apositioning device comprising:

a memory which is a ring buffer which includes a storage area capable ofstoring three or more cycles of a signal corresponding to at least aninversion time interval of a navigation message and in which a signalreceived by an RF reception circuit section which receives a GPSsatellite signal is sequentially stored while shifting a storageposition; and

a positioning section which reads the signal from the storage area whilechanging a signal read position, performs an acquisition and/or trackingprocess of the GPS satellite signal based on the read signal, andperforms a specific positioning process.

According to one embodiment of the invention, there is provided acomputer-readable storage medium storing a program for a positioningdevice including a memory which is a ring buffer which includes astorage area capable of storing three or more cycles of a signalcorresponding to at least an inversion time interval of a navigationmessage and in which a signal received by an RF reception circuitsection which receives a GPS satellite signal is sequentially storedwhile shifting a storage position, and a processor which can execute aprogram, the program causing the processor to function as a positioningsection which reads the signal from the storage area while changing asignal read position, performs an acquisition and/or tracking process ofthe GPS satellite signal based on the read signal, and performs aspecific positioning process.

According to the above configuration, the signal is read from thestorage area of the memory (ring buffer) which can store three or morecycles of a signal while changing the signal read position. The GPSsatellite signal is acquired and/or tracked based on the signal, and thespecific positioning process is performed. For example, a signal with asmall cancellation portion due to the polarity inversion of thenavigation message can be acquired by reading the signal whilesequentially changing the signal read position by one millisecond,whereby the sensitivity can be improved. Moreover, the processing timecan be reduced by reading the signal corresponding to the inversion timeinterval of the navigation message from the storage area into which thesignal is not written while writing the signal into the memory (ringbuffer), for example.

In the positioning device, the GPS satellite signal received by the RFreception circuit section may include a signal transmitted from each ofa plurality of satellites; and

the positioning section may change the signal read position in units ofacquisition and/or tracking target satellites.

In the storage medium, the GPS satellite signal received by the RFreception circuit section may include a signal transmitted from each ofa plurality of satellites; and

the positioning section may change the signal read position in units ofacquisition and/or tracking target satellites.

According to the above configuration, since the signal read position ischanged in units of acquisition and/or tracking target satellites, anappropriate signal can be read in units of satellites.

In the positioning device, the positioning section may include a readposition determination section which changes a read position at which asignal for a specific period of time is read from the storage area, anddetermines a read position from the memory used for a correlationprocess for acquiring the GPS satellite signal based on a signalstrength of the signal for the specific period of time read from each ofthe read positions; and

the positioning section may acquire the GPS satellite signal byperforming the correlation process for the signal read from thedetermined read position.

In the storage medium, the positioning section may include a readposition determination section which changes a read position at which asignal for a specific period of time is read from the storage area, anddetermines a read position from the memory used for a correlationprocess for acquiring the GPS satellite signal based on a signalstrength of the signal for the specific period of time read from each ofthe read positions; and

the positioning section may acquire the GPS satellite signal byperforming the correlation process for the signal read from thedetermined read position.

According to the above configuration, the read position from the memoryused for the correlation process for acquiring the GPS satellite signalis determined based on the signal strength of the signal for thespecific period of time read from the storage area of the memory whilechanging the read position. The GPS satellite signal is acquired byperforming the correlation process for the signal read from thedetermined read position. Therefore, the GPS satellite signal can beacquired by performing the correlation process for the signal read fromthe read position at which the signal strength is maximum, for example.

In the positioning device, the read position determination section mayinclude:

a set-unit signal strength calculation section which calculates a signalstrength of each of M (M≧2) specific-time signal sets obtained atintervals of a specific set-to-set offset time, one specific-time signalset including N (N≧2) specific-time signals obtained from the storagearea at intervals of a specific unit offset time;

a specific-time signal strength calculation section which calculates 1)the signal strength of each of the specific-time signals included in thespecific-time signal set having a maximum strength calculated by theset-unit signal strength calculation section, or 2) the signal strengthof each of the specific-time signals included in the specific-timesignal set having the maximum strength and the specific-time signalspreceding or subsequent to the specific-time signal set having themaximum strength; and

a determination section which determines the read position from thememory used for the correlation process based on the position of thememory at which the specific-time signal is stored which has the maximumstrength calculated by the specific-time signal strength calculationsection.

In the storage medium, the read position determination section mayinclude:

a set-unit signal strength calculation section which calculates a signalstrength of each of M (M≧2) specific-time signal sets obtained atintervals of a specific set-to-set offset time, one specific-time signalset including N (N≧2) specific-time signals obtained from the storagearea at intervals of a specific unit offset time;

a specific-time signal strength calculation section which calculates 1)the signal strength of each of the specific-time signals included in thespecific-time signal set having a maximum strength calculated by theset-unit signal strength calculation section, or 2) the signal strengthof each of the specific-time signals included in the specific-timesignal set having the maximum strength and the specific-time signalspreceding or subsequent to the specific-time signal set having themaximum strength; and

a determination section which determines the read position from thememory used for the correlation process based on the position of thememory at which the specific-time signal is stored which has the maximumstrength calculated by the specific-time signal strength calculationsection.

According to the above configuration, the signal set for the specificperiod of time is acquired from the storage area of the memory whilechanging the acquisition timing, and the signal strength of each signalset is calculated. The signal strength of each signal included in thesignal set having the maximum strength or the signal strength of each ofthe signals included in the signal set having the maximum strength andthe signals preceding or subsequent to the signal set having the maximumstrength are calculated, and the signal read position from the memoryused for the correlation process is determined based on the position ofthe memory at which the signal having the maximum strength is stored.The number of calculations and the calculation time can be reduced byacquiring the signal sets while changing the acquisition timing,determining the signal set having the maximum strength, and specifyingthe signal having the maximum strength, whereby the signal having themaximum strength can be efficiently specified. Moreover, the signalhaving the maximum strength can be accurately determined by searchingfor not only the signals included in the signal set having the maximumstrength, but also the signals preceding or subsequent to the signal sethaving the maximum strength.

According to one embodiment of the invention, there is provided apositioning device comprising:

a memory which is a ring buffer in which a signal received by an RFreception circuit section which receives a GPS satellite signal issequentially stored;

a set-unit signal strength calculation section which calculates a signalstrength of each of M (M≧2) specific-time signal sets obtained atintervals of a specific set-to-set offset time, one specific-time signalset including N (N≧2) specific-time signals obtained from the storagearea at intervals of a specific unit offset time;

a specific-time signal strength calculation section which calculates 1)the signal strength of each of the specific-time signals included in thespecific-time signal set having a maximum strength calculated by theset-unit signal strength calculation section, or 2) the signal strengthof each of the specific-time signals included in the specific-timesignal set having the maximum strength and the specific-time signalspreceding or subsequent to the specific-time signal set having themaximum strength; and

a determination section which determines the read position from thememory used for the correlation process based on the position of thememory at which the specific-time signal is stored which has the maximumstrength calculated by the specific-time signal strength calculationsection;

the positioning device acquiring the GPS satellite signal by reading thesignal from the read position determined by the determination sectionand performing the correlation process, and performing a specificpositioning process.

According to one embodiment of the invention, there is provided acomputer-readable storage medium storing a program for a positioningdevice including a memory which is a ring buffer in which a signalreceived by an RF reception circuit section which receives a GPSsatellite signal is sequentially stored, and a processor which canexecute a program, the program causing the processor to function as:

a set-unit signal strength calculation section which calculates a signalstrength of each of M (M≧2) specific-time signal sets obtained atintervals of a specific set-to-set offset time, one specific-time signalset including N (N≧2) specific-time signals obtained from the storagearea at intervals of a specific unit offset time;

a specific-time signal strength calculation section which calculates 1)the signal strength of each of the specific-time signals included in thespecific-time signal set having a maximum strength calculated by theset-unit signal strength calculation section, or 2) the signal strengthof each of the specific-time signals included in the specific-timesignal set having the maximum strength and the specific-time signalspreceding or subsequent to the specific-time signal set having themaximum strength;

a determination section which determines the read position from thememory used for the correlation process based on the position of thememory at which the specific-time signal is stored which has the maximumstrength calculated by the specific-time signal strength calculationsection; and

a positioning section which acquires the GPS satellite signal by readingthe signal from the read position determined by the determinationsection and performing the correlation process, and performs a specificpositioning process.

According to the above configuration, the signal set for the specificperiod of time is acquired from the memory (ring buffer) while changingthe acquisition timing, and the signal strength of each signal set iscalculated. The signal strength of each signal included in the signalset having the maximum strength or the signal strength of each of thesignal included in the signal set having the maximum strength and thesignals preceding or subsequent to the signal set having the maximumstrength are calculated, and the read position from the memory used forthe correlation process is determined based on the position of thememory at which the signal having the maximum strength is stored. TheGPS satellite signal is acquired based on the signal read from thedetermined read position, and the specific positioning process isperformed.

According to one embodiment of the invention, there is provided anelectronic instrument comprising one of the above positioning devices.

A portable telephone including a positioning device and having anavigation function is described below with reference to the drawings asone embodiment of an electronic instrument. Note that the embodiments towhich the invention can be applied are not limited thereto.

1. Configuration and Operation

FIG. 1 is a block diagram showing the functional configuration of aportable telephone 1 according to this embodiment. The portabletelephone 1 includes a GPS antenna 10, a GPS reception section 20, ahost central processing unit (CPU) 110, an operation section 120, adisplay section 130, a portable wireless communication section 140, aread only memory (ROM) 150, and a random access memory (RAM) 160.

The GPS antenna 10 is an antenna which receives an RF signal including aGPS satellite signal transmitted from a GPS satellite, and outputs thereceived RF signal to the GPS reception section 20.

The GPS reception section 20 includes a surface acoustic wave (SAW)section 30, a low noise amplifier (LNA) 40, a temperature-compensatedcrystal oscillator (TCXO) 50, a radio frequency (RF) reception circuitsection 60, a memory 70, and a baseband process circuit section 80. TheGPS reception section 20 forms a positioning device 100 which is acharacteristic configuration according to this embodiment.

The RF reception circuit section 60 and the baseband process circuitsection 80 of the GPS reception section 20 may be manufactured asdifferent large scale integrated (LSI) circuits, or may be integrated onone chip. The entire GPS reception section 20 including the SAW section30, the LNA 40, the TCXO 50, and the memory 70 may be integrated on onechip.

The SAW section 30 is a bandpass filter which allows only a specificfrequency band component of the RF signal received through the GPSantenna 10 to pass through, and outputs the signal which has passedtherethrough to the LNA 40.

The LNA 40 is a low noise amplifier which amplifies the signal which haspassed through the SAW section 30, and outputs the amplified signal tothe RF reception circuit section 60.

The TCXO 50 is a temperature-compensated crystal oscillator whichgenerates an oscillation signal having a specific oscillation frequency,and outputs the generated oscillation signal to the RF reception circuitsection 60.

The RF reception circuit section 60 generates an RF signalmultiplication oscillation signal by dividing or multiplying thefrequency of the oscillation signal input from the TCXO 50. The RFreception circuit section 60 down-converts the RF signal which haspassed through the GPS antenna 10, the SAW section 30, and the LNA 40into an intermediate-frequency signal (hereinafter called “IF signal”)by multiplying the generated oscillation signal by the signal amplifiedby the LNA 40. After subjecting the IF signal to amplification and thelike, the RF reception circuit section 60 converts the IF signal into adigital signal using an A/D converter, and outputs the digital signal tothe memory 70.

The memory 70 is a buffer which stores the IF signal output from the RFreception circuit section 60. The configuration of the memory 70 isdescribed later in detail.

The baseband process circuit section 80 is a circuit section whichacquires/extracts the GPS satellite signal from the IF signal stored inthe memory 70, decodes the data of the signal to acquire the navigationmessage, time information, and the like, and performs pseudo-rangecalculations, positioning calculations, and the like.

FIG. 2 is a view illustrative of the outline of a process performed bythe baseband process circuit section 80. The baseband process circuitsection 80 determines the position at which the baseband process circuitsection 80 starts to read the IF signal sequentially stored in thememory 70 (hereinafter called “signal read position”).

The baseband process circuit section 80 acquires the GPS satellitesignal based on the IF signal read from the determined signal readposition. The baseband process circuit section 80 acquires the GPSsatellite signal by extracting the GPS satellite signal from the IFsignal. This process is implemented by subjecting the IF signal to fastFourier transform (FFT) calculations and the like and performing acorrelation process. In more detail, the baseband process circuitsection 80 calculates the correlation value of a pseudo-generated spreadcode (code replica) and the IF signal by performing a coherentaccumulation process.

When the GPS satellite signal has been acquired, the baseband processcircuit section 80 tracks the acquired GPS satellite signal. Thebaseband process circuit section 80 tracks the GPS satellite signals bysynchronously holding the acquired GPS satellite signals in parallel.For example, this process is implemented by tracking the phases of theC/A code and the carrier contained in the satellite signal using a codeloop known as a delay locked loop (DLL) and a carrier loop known as aphase locked loop (PLL).

The baseband process circuit section 80 then decodes the data of the GPSsatellite signal to acquire the navigation message, and locates thepresent position of the portable telephone 1 by performing pseudo-rangecalculations, positioning calculations, and the like (hereinafter called“positioning process”).

The configuration of the memory 70 which is a characteristic portionaccording to this embodiment and the principle of the signal readposition determination process performed by the baseband process circuitsection 80 are described below.

FIG. 3A is a view showing the configuration of the memory 70, and FIGS.3B and 3C are views illustrative of an operation of writing the signalinto the memory 70. The memory 70 includes storage areas M1 to M3, eachof which can store a signal of which one cycle is 20 milliseconds. TheIF signal output from the RF reception circuit section 60 issequentially and consecutively stored in the storage areas M1 to M3 inorder proceeding from the storage area M1. Specifically, the storageareas M1 to M3 are utilized as banks to which consecutive addresses areassigned.

Specifically, the position at which the signal is written (hereinaftercalled “write position”) at a time T=0 is the head position of thestorage area M1 (FIG. 3B). The write position proceeds toward thestorage area M2 with the lapse of the time T (FIG. 3C). When the signalhas been written into the entire storage area M3, the write positionreturns to the head position of the storage area M1. Specifically, thememory 70 is a ring buffer.

In the following description, a time length of 20 milliseconds of eachstorage area is called a “record”. The present signal write targetstorage area of the memory 70 is called a “write area”, and the storagearea other than the write area from which the written signal can be readis called a “readable area”.

FIG. 4 is a view illustrative of the concept of a slice. FIG. 4 is aview illustrative of an operation of writing the signal into the memory70 and an operation of reading the signal stored in the memory 70. InFIG. 4, the signals have been written into the storage areas M2 and M3at the time t=0. In FIG. 4, the upper portion (1) indicates the signalwrite operation, and the lower portion (2) indicates the signal readoperation. The write (acquisition) timing of the received signal israrely in synchronization with the inversion timing of the navigationmessage. In FIG. 4, the inversion timing of the navigation messageoccurs in the middle of each record.

In FIG. 4, the write position at the time t=0 is the head address of thestorage area M1, and the storage area M1 is the write area from the timet=0 to the time t=20 (millisecond). Therefore, the storage areas M2 andM3 are readable areas in this period. The signal is read from thereadable area as follows. Specifically, the head address of the readablearea in which the signal has been stored first is determined to be a“read reference position”. The data of one record is read while movingthe read position away from the read reference position.

A plurality of readable areas are considered to be one area, and thedata is read while moving the read position away (offset) from the headaddress (read reference position) of that area. For example, the readreference position in the period from the time t=0 to the time t=20(millisecond) in FIG. 4 is the head address of the storage area M2. Thereadable areas M2 and M3 are considered to be one area, and the signalis read from that area.

In the following description, the amount of offset from the readreference position is called a “read offset”. The read offset isdetermined in millisecond units. Note that the read offset actuallyindicates the amount of address offset of the memory.

The signal read operation and the slice are described in more detailwith reference to FIG. 4. The signal is read in units of signals (data)of 20 milliseconds which is the inversion cycle of the navigationmessage. The signal of 20 milliseconds read from the memory 70 is calleda “slice”.

The slice is read from the position separated from the read referenceposition by the read offset which is changed by a specific unit offsettime (millisecond). For example, when the unit offset time is onemillisecond and the signal is sequentially read for 20 millisecondswhile changing the read offset by one millisecond, twenty slices (i.e.,zeroth slice to nineteenth slice) shown in FIG. 4 are obtained in total.

FIG. 5 is a view illustrative of the signal read operation of thebaseband process circuit section 80 according to this embodiment. Thebaseband process circuit section 80 reads the signal according to theabove-described procedure. When the baseband process circuit section 80has read N (hereinafter called “set-forming slice count”) signalsspecified in advance, the baseband process circuit section 80 combinesthe slices to form a slice set.

The baseband process circuit section 80 changes the read offset from theread offset of the first slice included in the slice set by a specificset-to-set offset time (millisecond), and reads the signal according tothe same procedure as described above to form the next slice set. Thebaseband process circuit section 80 repeats the above procedure until atime length of 20 milliseconds is covered to obtain M (hereinaftercalled “slice set count”) slice sets in total.

For example, when the unit offset time is one millisecond, theset-forming slice count is three, and the set-to-set offset time is fivemilliseconds, four slice sets (i.e., zeroth slice set to third sliceset) shown in FIG. 5 are obtained in total. In this case, the slice setcount M is four.

The baseband process circuit section 80 calculates the total value ofthe signal strengths of the slices included in the slice set(hereinafter called “signal strength total value”) in units of the Mslice sets, and specifies the slice set having the maximum signalstrength total value (hereinafter called “maximum strength slice set”).In FIG. 5, since the slices included in the second slice set have theminimum cancellation portion due to the polarity inversion of thereceived signal (navigation message), the second slice set has themaximum signal strength total value. Therefore, the second slice set isthe maximum strength slice set.

The signal strength of the slice can be calculated using a coherentaccumulation process, for example. The coherent accumulation process isa calculation process of coherently summing up the sums of squares ofthe components I and Q of the signal over a specific coherentaccumulation time (e.g. 20 milliseconds).

The baseband process circuit section 80 sets a specific read targetrange including the position at which the maximum strength slice set isstored, and reads the signal within the read target range while changingthe read offset from the read reference position by the unit offsettime. The baseband process circuit section 80 calculates the signalstrength of each acquired slice, and specifies the slice with themaximum signal strength (hereinafter called “maximum strength slice”).

FIG. 6 is a view illustrative of the read target range, and shows someof the slice sets shown in FIG. 5. The starting point of the read targetrange is the position obtained by adding the unit offset time to theread offset of the last slice included in the slice set preceding themaximum strength slice set. The end point of the read target range isthe position obtained by subtracting the unit offset time from the readoffset of the first slice included in the slice set subsequent to themaximum strength slice set. In FIG. 6, a range of six milliseconds fromthe starting point S to the end point E is the read target range, andthe signal strengths of seven slices in total read from the read targetrange are calculated.

After specifying the maximum strength slice, the baseband processcircuit section 80 determines the read offset of the maximum strengthslice to be the maximum strength read offset. The baseband processcircuit section 80 then determines the area of the memory 70 into whichthe signal is currently written (write area) to determine the area fromwhich the signal can be read (readable area). The baseband processcircuit section 80 considers a plurality of readable areas to be onearea, and determines the position separated from the head address (readreference position) by the maximum strength read offset to be the signalread position.

The calculation results of the signal strength of the slice whilechanging the read offset are described below.

FIG. 7A is a view showing the results obtained in an environment inwhich a high-strength signal can be received from the GPS satellite(hereinafter called “strong electric field environment”), and FIG. 7B isa view showing the results obtained in an environment in which ahigh-strength signal cannot be received from the GPS satellite(hereinafter called “weak electric field environment”). In FIGS. 7A and7B, the horizontal axis indicates the read offset (millisecond), and thevertical axis indicates the signal strength of the slice and the signalstrength total value of the slice set.

Data D1 indicates the results of the signal strengths of twenty slicesobtained when the unit offset time is set at one millisecond. Theresults indicate that the signal strength of the slice when the readoffset is 13 milliseconds is maximum. Therefore, it is estimated thatthe position separated from the read reference position by a read offsetof 13 milliseconds corresponds to the polarity inversion position of thereceived signal (navigation message).

Data D2 indicates the results of the signal strength total values of sixslice sets when the unit offset time is set at one millisecond, theset-to-set offset time is set at three milliseconds, and the set-formingslice count is set at three. In this case, the signal strength totalvalue of the slice set when the read offset is 13 milliseconds ismaximum. This indicates that the polarity inversion position of thereceived signal (navigation message) can be accurately estimated usingthe method according to this embodiment.

The method according to this embodiment is particularly useful for theweak electric field environment. As is clear from the results shown inFIG. 7B, when separately calculating the signal strengths of twentyslices, since the slices show a small variation in signal strength, itis difficult to identify the maximum strength. Therefore, it isdifficult to specify the maximum strength slice compared with the strongelectric field environment.

On the other hand, the signal strength total values of the slice setsshow a large variation since the signal strengths of three slices ofeach slice set are summed up. Therefore, the maximum strength slice setcan be easily specified. Since the maximum strength slice is likely tobe included in the maximum strength slice set, it is possible toefficiently search for the maximum strength slice.

As is clear from the number of plots shown in FIGS. 7A and 7B, thenumber of signal strength calculations is smaller for the data D2 thanthe data D1. Specifically, the number of calculations and thecalculation time can be reduced by determining the maximum strengthslice set utilizing the slice sets and specifying the maximum strengthslice, whereby the maximum strength slice can be efficiently specified.

The baseband process circuit section 80 includes a circuit whichperforms the correlation process, a circuit which generates the spreadcode (code replica) for performing correlation calculations, a circuitwhich decodes data, a CPU 81 which controls each section of the basebandprocess circuit section 80 and the RF reception circuit section 60 andperforms various calculations including a baseband process describedlater, a ROM 83, and a RAM 85.

FIGS. 8A and 8B are views showing examples of data stored in the ROM 83and the RAM 85 included in the baseband process circuit section 80. TheROM 83 stores a baseband process program 831 which is read by the CPU 81and executed as the baseband process (see FIG. 11). A maximum strengthread offset determination program 832 executed as a maximum strengthread offset determination process (see FIG. 12) is included in thebaseband process program 831 as a subroutine.

The baseband process is a process in which the CPU 81 determines thesignal read position of the signal received from each acquisition targetGPS satellite (hereinafter called “acquisition target satellite”),performs an acquisition/tracking process of the GPS satellite signal, anavigation message decoding process, and the like based on the signalread from the signal read position, and locates the present position ofthe portable telephone 1. The baseband process is described later indetail using a flowchart.

The maximum strength read offset determination process is a process inwhich the CPU 81 sequentially reads the signal stored in the memory 70to form slice sets, and specifies the maximum strength slice based onthe signal strength total value of each slice set to determine themaximum strength read offset. The maximum strength read offsetdetermination process is also described later in detail using aflowchart.

The RAM 85 stores satellite-unit signal strength total value data 851,satellite-unit signal strength data 853, satellite-unit maximum strengthread offset data 855, satellite data 857, and positioning data 859.

The satellite-unit signal strength total value data 851 is data in whichthe signal strength total value of each slice set acquired from thememory 70 is stored in units of acquisition target satellites. Thesatellite-unit signal strength total value data 851 is updated each timethe signal strength total value of the slice set is calculated in themaximum strength read offset determination process.

The satellite-unit signal strength data 853 is data in which the signalstrength of each slice acquired from the memory 70 is stored in units ofacquisition target satellites. The satellite-unit signal strength data853 is updated each time the signal strength of the slice is calculatedin the maximum strength read offset determination process.

FIG. 9 is a view showing a data configuration example of thesatellite-unit maximum strength read offset data 855. An acquisitiontarget satellite number 8551 and a maximum strength read offset 8553determined for the acquisition target satellite are stored as thesatellite-unit maximum strength read offset data 855 while beingassociated with each other. The satellite-unit maximum strength readoffset data 855 is updated when the maximum strength read offset isdetermined in the maximum strength read offset determination process.

FIG. 10 is a view showing a data configuration example of the satellitedata 857. An acquisition target satellite number 8571 and satelliteinformation 8573 including the position, the velocity, and the movingdirection of the acquisition target satellite are stored as thesatellite data 857 while being associated with each other. The positionof the acquisition target satellite is indicated by three-dimensionalcoordinates in the terrestrial reference frame, and the moving directionis indicated by a three-dimensional unit vector in the terrestrialreference frame, for example. The satellite data 857 is updated eachtime the satellite information is calculated in the baseband process.

The positioning data 859 is data of the located position of the portabletelephone 1. For example, three-dimensional coordinates in theterrestrial reference frame are stored as the positioning data 859. Thepresent position located by the positioning process during the basebandprocess is stored as the positioning data 859 in time series.

The host CPU 110 is a processor which controls each section of theportable telephone 1 according to various programs such as a systemprogram stored in the ROM 150. The host CPU 110 mainly controls thetelephone function and causes the display section 130 to display anavigation screen in which the present position of the portabletelephone 1 located by the baseband process circuit section 80 isplotted.

The operation section 120 is an input device including an operation key,a button switch, and the like, and outputs a press signal to the hostCPU 110. Various instruction inputs such as a telephone call request ora navigation screen display request are performed by operating theoperation section 120.

The display section 130 is a display device which includes a liquidcrystal display (LCD) or the like and displays various images based on adisplay signal input from the host CPU 110. The display section 130displays date/time information, the navigation screen, and the like.

The portable wireless communication section 140 is a known communicationcircuit section implemented by an antenna through which a radio signalis transmitted and received between the portable wireless communicationsection 140 and a radio base station installed by a portable telephonecommunication service provider, an RF converter, and the like. Theportable wireless communication section 140 transmits and receives aradio signal under control of the host CPU 110 to implement a telephonecall and e-mail transmission/reception.

The ROM 150 is a read-only storage device. The ROM 150 stores data andvarious programs such as a system program for controlling the portabletelephone 1, a program for implementing a telephone call and e-mailtransmission/reception, and a program for implementing a navigationfunction. The host CPU 110 performs the processes according to theseprograms and data.

The RAM 160 is a readable/writable storage device. The RAM 160 forms awork area for temporarily storing the system program executed by thehost CPU 110, various programs, data during various processes,processing results, and the like.

2. Process Flow

FIG. 11 is a flowchart showing the flow of the baseband processperformed by the baseband process circuit section 80 by causing the CPU81 to read and execute the baseband process program 831 stored in theROM 83. In the baseband process, after reception of the RF signalthrough the GPS antenna 10, down-conversion of the RF signal into the IFsignal by the RF reception circuit section 60, and the like, the GPSreception section 20 is in a state in which the data of the signal isstored in the memory 70 at any time.

The CPU 81 performs the following initial settings (step A1).Specifically, the CPU 81 sets specific values as the unit offset time,the set-to-set offset time, the set-forming slice count, and the sliceset count.

The CPU 81 performs the acquisition target satellite determinationprocess (step A3). Specifically, the CPU 91 determines the GPS satellitefrom which the signal can be received based on the orbital informationof the GPS satellite such as an almanac, and adds a new acquisitiontarget satellite or excludes a GPS satellite considered to be positionedoutside the acquisition range from the acquisition target satellites.

The CPU 81 executes a loop A in units of the acquisition targetsatellites (steps A5 to A19). In the loop A, the CPU 81 determineswhether or not the maximum strength read offset of the acquisitiontarget satellite has been determined (step A7). When the CPU 81 hasdetermined that the maximum strength read offset of the acquisitiontarget satellite has been determined (step A7: Yes), the CPU 81transitions to the step A11.

When the CPU 81 has determined that the maximum strength read offset ofthe acquisition target satellite has not been determined (step A7: No),the CPU 81 performs the maximum strength read offset determinationprocess by reading and executing the maximum strength read offsetdetermination program 832 stored in the ROM 83 (step A9).

FIG. 12 is a flowchart showing the flow of the maximum strength readoffset determination process.

The CPU 81 determines the present signal write target storage area to bethe write area (step B1). The CPU 81 then determines the readable areaof the memory 70 (step B3). Specifically, the CPU 81 determines thestorage area excluding the write area to be the readable area.

The CPU 81 sequentially reads the signal from the position obtained byadding the read offset to the read reference position of the readablearea while changing the read offset to form a slice set (step B5), andcalculates the signal strength total value of each slice set (step B7).The CPU 81 stores the calculated signal strength total value as thesatellite-unit signal strength total value data 851 in the RAM 85 whileassociating the signal strength total value with the acquisition targetsatellite number.

The CPU 81 specifies the maximum strength slice set (step B9), and setsa specific range including the maximum strength slice set to be the readtarget range (step B11). The read target range is set using the methoddescribed with reference to FIG. 6.

The CPU 81 reads the signal from the position within the set read targetrange obtained by adding the read offset to the read reference positionwhile changing the read offset by the unit offset time to sequentiallyacquire slices (step B13). The CPU 81 calculates the signal strength ofeach acquired slice (step B15).

The CPU 81 specifies the maximum strength slice (step B17), anddetermines the read offset of the maximum strength slice to be themaximum strength read offset 8553 (step B19). The CPU 81 stores thedetermined maximum strength read offset 8553 as the satellite-unitmaximum strength read offset data 855 in the RAM 85 while associatingthe maximum strength read offset 8553 with the acquisition targetsatellite number 8551, and finishes the maximum strength read offsetdetermination process.

Again referring to the baseband process shown in FIG. 11, aftercompletion of the maximum strength read offset determination process,the CPU 81 performs the signal read position determination process (stepA11). Specifically, the CPU 81 determines the present write area of thememory 70, and determines the storage area excluding the write area tobe the readable area. The CPU 81 considers a plurality of readable areasto be one area, and determines the position obtained by adding themaximum strength read offset to the head address of that area to be thesignal read position.

The CPU 81 acquires/tracks the GPS satellite signal (step A13).Specifically, the CPU 81 reads the IF signal stored in the memory 70from the signal read position determined by the signal read positiondetermination process, and extracts the GPS satellite signal bysubjecting the read IF signal to FFT calculations and the like andperforming the correlation process.

In more detail, the CPU 81 calculates the correlation value of the IFsignal read from the signal read position and the spread code byperforming the coherent accumulation process, and specifies the carrierfrequency of the received signal by extracting the frequency componentwith the largest amplitude. The CPU 81 synchronously holds the extractedGPS satellite signals in parallel using the code loop and the carrierloop.

The CPU 81 decodes the data of the acquired GPS satellite signal toacquire the navigation message (step A15), and calculates the position,the velocity, and the moving direction of the acquisition targetsatellite based on the navigation message to obtain the satelliteinformation 8573 (step A17). The CPU 81 stores the calculated satelliteinformation 8573 as the satellite data 857 in the RAM 85 whileassociating the satellite information 8573 with the acquisition targetsatellite number 8571, and processes the next acquisition targetsatellite.

After the CPU 81 has performed the process in the steps A7 to A17 forall of the acquisition target satellites, the CPU 81 finishes the loopA. The CPU 81 performs known positioning calculations based on thesatellite information 8573 of each acquisition target satellitecalculated in the step A17, and locates the present position of theportable telephone 1 (step A21). The CPU 81 stores the located presentposition as the positioning data 859 in the RAM 85.

The CPU 81 determines whether or not to finish the process (step A23).Specifically, the CPU 81 finishes the process when a process finishinstruction signal is input from the host CPU 110 in response to aninstruction operation disabling the navigation function or aninstruction operation removing power from the portable telephone 1 usingthe operation section 120, for example.

When the CPU 81 has determined to continue the process (step A23: No),the CPU 91 returns to the step A3. When the CPU 81 has determined tofinish the process (step A23: Yes), the CPU 81 finishes the basebandprocess.

3. Effect

According to this embodiment, a slice set for a specific period of timeis acquired from the storage area of the memory 70 (ring buffer) whilechanging the read position, and the signal strength total value of eachslice set is calculated. The signal strengths of the slices included inthe maximum strength slice set and the signal strengths of the slicespreceding or subsequent to the maximum strength slice set arecalculated, and the final signal read position is determined based onthe read offset of the maximum strength slice. The GPS satellite signalis acquired/tracked based on the slice read from the determined signalread position, and the specific positioning process is then performed.

Since the maximum strength slice is a slice having the smallestcancellation portion due to the polarity inversion of the receivedsignal, sensitivity can be improved by determining the final signal readposition based on the read offset of the maximum strength slice.Moreover, since the signal is read from the storage area into which thesignal is not written while writing the signal into the memory 70 (ringbuffer), the processing time can be reduced.

The number of calculations and the calculation time can be reduced byacquiring the slice sets while changing the acquisition timing,determining the maximum strength slice set, and specifying the maximumstrength slice, whereby the maximum strength slice can be efficientlyspecified. The maximum strength slice can be accurately determined bysearching for not only the slices included in the maximum strength sliceset, but also the slices adjacent to the maximum strength slice set.

4. Modification

4-1. Application Example

The invention may be applied to various electronic instruments such as apersonal digital assistant (PDA), a portable navigation system, and acar navigation system in addition to the portable telephone.

4-2. Processor

This embodiment has been described above taking an example in which theprocessor which controls the baseband process circuit section 80 is aCPU. Note that the processor may be a digital signal processor (DSP),for example.

4-3. Memory

This embodiment has been described above taking an example in which thememory 70 includes three storage areas. Note that four or more storageareas may be provided so that four or more cycles of signals can bestored. In this case, the signal write/read operations are the same asdescribed above.

4-4. Host CPU

The host CPU 110 may perform some or all of the processes performed bythe CPU 81 of the baseband process circuit section 80 by means ofsoftware. For example, the host CPU 110 may perform the maximum strengthread offset determination process and the signal read positiondetermination process, and the CPU 81 of the baseband process circuitsection 80 may perform the acquisition/tracking process of the GPSsatellite signal, the positioning process, and the like by reading thesignal stored in the memory 70 from the signal read position determinedby the host CPU 110. The host CPU 110 may perform the positioningprocess based on the GPS satellite signal acquired/tracked by the CPU81.

4-5. Parameter

The unit offset time, the set-to-set offset time, the set-forming slicecount, and the slice set count described in this embodiment are onlyexamples, and may be appropriately set. For example, the set-to-setoffset time may be set at one millisecond, and the maximum strengthslice may be specified from the slices of the maximum strength sliceset.

4-6. Signal Strength Average Value

This embodiment has been described above taking an example in which themaximum strength slice set is specified based on the signal strengthtotal values of the slice sets. Note that the average value of thesignal strengths of the slices included in the slice set (hereinaftercalled “signal strength average value”) may be calculated instead of thesignal strength total value, and the slice set having the maximum signalstrength average value may be specified.

Although only some embodiments of the invention have been describedabove in detail, those skilled in the art would readily appreciate thatmany modifications are possible in the embodiments without materiallydeparting from the novel teachings and advantages of the invention.Accordingly, such modifications are intended to be included within thescope of the invention.

1. A receiver comprising: a reception circuit section that receives asignal from a positioning satellite; a memory that stores a receivedsignal that has been received by the reception circuit section; aset-unit signal strength calculation section that calculates a signalset having a maximum signal strength from a plurality of signal sets,each of the plurality of signal sets including two or more receivedsignals for a specific period of time that differ in storage position inthe memory; a specific-time signal strength calculation section thatcalculates a received signal for the specific period of time having themaximum signal strength from the received signals for the specificperiod of time included in the signal set having the maximum signalstrength and the received signals stored at storage positions precedingor subsequent to that of the signal set having the maximum signalstrength; and a determination section that determines a read startposition of the received signal for the specific period of timecalculated by the specific-time signal strength calculation section tobe a read start position used for a correlation process for acquiringthe signal from the positioning satellite.
 2. The receiver as defined inclaim 1, the set-unit signal strength calculation section calculatingthe signal set having the maximum signal strength from M (M≧2) signalsets stored at storage positions that differ by a specific set-to-setoffset time, each of the plurality of signal sets including N (N≧2)received signals for the specific period of time that are stored atstorage positions that differ from a reference position at intervals ofa specific unit offset time.
 3. An electronic instrument comprising thereceiver as defined in claim
 1. 4. An electronic instrument comprisingthe receiver as defined in claim 2.